Power steering systems in vehicles often employ assist algorithms that are non-linear in nature. Such systems apply different amounts of torque to turn the wheels of vehicles in which they are employed depending upon the driving conditions, speed of the vehicle, and user input. During the application of the differing amounts of torque, it is desirable that the system provide a smooth and linear tactile response at the steering wheel. It may be desirable to use different damping values in the control system depending on the inputs to the system to result in a linear tactile response.
In operation, a user applies an amount of torque, generally manually, to a steering input device at a particular velocity. The steering input device transfers this torque and velocity to a motor that responsively turns the wheels of the vehicle through appropriate linkages. The applied torque and the velocity of the steering wheel are input into a controller that controls the motor. The controller applies damping signals to the motor to provide a smooth, linear tactile response for the user when the user turns the steering wheel.
Users apply different torque at different velocities to the steering wheel while controlling the vehicle. For example, when initiating a left turn, the user turns the steering wheel to the left thereby applying a positive torque at a positive velocity to the motor. While in the left turn, a user may adjust the arc of the turn by moving the steering wheel slightly to the right. The movement of the steering wheel slightly to the right applies a positive torque and at a negative velocity to the motor. Since the movement of the steering wheel to initiate a turn and the slight movement of the steering wheel that is used to adjust the turn are different, it is desirable that the damping used during the two motions be different in order to effect a smooth tactile feel to the user. The use of different damping depending on the operation of the steering wheel may be implemented using quadrant damping.
FIG. 1 illustrates a prior art example of steering quadrants. The graph includes a y-axis defined as the motor velocity and an x-axis defined as the hand wheel torque. Quadrant I is defined as a motor operating condition wherein the applied torque signal and the motor velocity are both positive. Point 301 is an example of an input in Quadrant I. Quadrant II is defined as a motor operating condition wherein the applied torque signal is positive, but the motor velocity is negative. In quadrant III, the applied torque signal and the motor velocity are both negative. In Quadrant IV, the applied torque signal is negative, but the motor velocity is positive. Quadrant III mirrors Quadrant I, but with opposite signs for motor velocity and applied torque signals. Similarly, Quadrant IV mirrors Quadrant II, but with opposite signs for motor velocity and applied torque signals.